The present invention is directed to electrostatic chucks for holding and positioning semiconductor substrates within process chambers during substrate processing operations.
Electrostatic chucks are used in semiconductor fabrication processes to hold substrates during processing of the substrates. A typical electrostatic chuck comprises a base adapted to be secured to a support in a process chamber. An insulator with an electrode embedded therein, is on the base. Typically, the insulator is an insulative polymer such as a polyimide, and the electrode is an electrically conductive metal layer. An electrical connector electrically connects the electrode in the insulator to a voltage supply source in the process chamber. When a substrate is placed on the chuck, and the voltage supply used to electrically bias the electrode in the insulator, opposing electrostatic charge accumulates in the substrate and the electrode resulting in attractive electrostatic forces that hold the substrate to the chuck. Electrostatic chucks are generally described in, for example U.S. patent application Ser. Nos. 08/278,787 by Cameron, et al.; 08/276,735 by Shamouilian, et al.; and 08/189,562, by Shamouilian, et al.--all of which are incorporated herein by reference.
Conventional electrostatic chucks also have cooling systems for cooling the substrate held on the chuck. However, conventional cooling systems do not adequately cool the perimeter of the substrate because the cooling systems stop short of, and do not extend to, the peripheral edge of the chuck. For example, U.S. patent application Ser. Nos. 08/276,735 and 08/189,562, both by Shamouilian, et al., describe a coolant system comprising coolant grooves which extend through the insulator and electrode on the chuck, and hold a coolant for cooling the substrate. When a substrate is held on the chuck, the substrate covers and seals the coolant grooves so that the coolant held in the grooves does not leak out. The coolant grooves stop short of the peripheral edge of the insulator, forming a relatively large edge gap between the grooves and the peripheral edge of the insulator, the edge gap often exceeding 10 to 20 mm. The large edge gap is provided to allow the overlying substrate to effectively cover and seal the coolant grooves so that coolant does not leak out from the grooves. However, because no coolant is held in the edge gap, the overlying perimeter of the substrate may be less effectively cooled compared to central portions of the substrate. Thus a risk of overheating which can damage the integrated circuits processed on the substrate and reduce effective yields from the substrate may exist in these chucks.
Another limitation of conventional chucks is the weak electrostatic attractive force that is obtained from electrodes having reduced surface areas. The area of the electrode in conventional chucks is often reduced by features which extend and cut through the electrode, such as for example, the coolant grooves of the afore described chuck cooling system which cut through the electrode. The reduced electrode area lowers the electrostatic clamping force exerted by the electrode when the electrode is electrically biased. Weak electrostatic clamping force can result in movement or misalignment of the substrate during processing, which can result in loss of the entire substrate at a cost of several thousands of dollars. Weak clamping force can also cause coolant to leak out from the coolant grooves covered by the substrate.
Another problem of existing chucks is the limited lifetime of the chucks in erosive environments. The use of polymers, such as polyimide, to insulate the electrode of the electrostatic chuck limits the useful lifetime of the chuck in erosive semiconductor fabrication processes, particularly in processes which use oxygen or halogen containing gases and plasmas. Oxygen and halogen containing gases and plasmas are used for a variety of tasks, including etching of substrates and cleaning of process chambers. These gases form erosive environments which can rapidly erode the exposed polyimide portions of the insulator on the chuck. While a large portion of the insulator on the chuck is covered by the substrate held on the chuck and thereby protected from the erosive environment, the peripheral edge of the insulator is still exposed to the erosive environment. The exposed peripheral edge of the insulator can erode in as few as a thousand process cycles. Erosion even at a single point on the peripheral edge of the insulator can expose the electrode in the chuck, causing failure of the chuck by short circuiting of the electrode. Failure of the insulated electrode requires replacement of the entire chuck which is expensive and slows down the fabrication process. Therefore, it is desirable to have an electrostatic chuck that demonstrates reduced erosion.
Thus it is desirable to have an electrostatic chuck which provides improved cooling for the substrate held on the chuck. It is also desirable for the chuck to have increased electrostatic clamping force for holding the substrate on the chuck. It is further desirable to have a chuck with improved erosion resistance.